Discharge tube for ultrahigh frequencies



April 23, 1957 E. LABIN 2,790,106

DISCHARGE TUBE FOR ULTRAHIGH FREQUENCIES Filed April 23, 1951 3 Sheets-Sheet 1 lNVENT-OR EDOU ARD LABIN AGENT April 23, 1957 I E. LABlN 2,790,106

DISCHARGE TUBE FOR ULTRAHIGH FREQUENCIES Filed April 25, 1951 3 Sheets-Sheet 2 INVENTOR EDOUARD LABIN AGENT April 23, 1957 I LABlN 2,790,106

DISCHARGE TUBE FOR ULTRAHIGH FREQUENCIES Filed'April 23, 1951 3 Sheets-Sheet 3 I'NVENTOR EDOUARD LABIN Unitfid States Pat n DISCHARGE TUBE FOR ULTRAHIGH FREQUENCIES Edouard Labin, Paris, France, assignor, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application x rnzs', .1951,.SerialNo..222,489 Claims priority, application France May 2, .1950

' 3 Claims. (Cl. SIS-5.18)

This invention relates to a device comprising an electric discharge tube for very high frequencies in which'an electronbeam is produced, the speed .ofthe electrons .in the beam being governed by an ultra-high frequency oscillation with the use of a modulation electrode system, whereupon'the speed variations are converted into intensity variations with the use of a brake field electrode system which causes the movement of the speed-varied electrons to reverse its direction during the conversion of the speed variations into intensity variations, a second brake field electrode system being arranged between the cathode and the control electrode system.

In addition, the invention relates to a tube for such a device.

In the known devices of the kind indicated above the modulation electrodes are generally web-shaped and the electrons are bunched by a magnet field. The electrons pass several times back and forth in an approximately parabolic field before being collected by the electrode system. The number of times the electrons are capable of passing back and forth and the high-frequency energy they are thus capable of giving off depends on the extent of bunching by the magnet field and on the lateral dispersion due to the space charge in the beam. In order to increase the efiiciency as far as possible and yet to be capable of producing greater energies by the use of greater beam currents it is advisable for the lateral dispersion in the beam to be reduced as far as possible. On the other hand, however, the presence of the magnet field is often an undesirable complication.

According to the invention, in a device comprising an electric discharge tube for very high frequencies in which an electron beam is produced, the speed of the electrons in the beam being governed by an ultra-high frequency oscillation with the use of a modulation electrode system, whereupon the speed variations are converted into intensity variations with the use of a brake field electrode system which causes the movement of the speed-varied electrons to reverse their direction during the conversion of the speed variations into intensity variations, and in which the cathode and the control electrode system are separated by a second brake field electrode system such that the electrons move back and forth in a parabolic field, all the electrodes have rotation-a1 symmetry about the same axis and they coincide at least in part with the equipotential surfaces of a potential distribution which is such that on a cylinder surface the field is parabolic in the axial direction and the radial field intensity is equal to zero. The cathode is therefore annular so that a hollow cylindrical electron beam of suitable diameter is produced. The above-mentioned potential distributions have in addition at least one equipotential surface of two sheets and the best results are obtained by the use of a device according to the invention, if the modulation electrodes, which may determine a cavity resonator of toroidal form, are caused to coincide at least in part with the said equipotential surface of two sheets. Due to the fact that 2,790,106 I Patented Arm "11957 the radial field intensity at the area of the electron beam is equal tozero, a'magnet field is not required tov concentrate the beam.

border that the invention may be more clearly understood and readily carried into effect, it will now be .described in greater detail with reference to the accompanying drawing, in which:

Fig. 1 is a graph of a definite potential distribution for a device according to the invention in a meridian plane of this potential distribution, and

Figs. 2 and 3'show electrode systems accordingito the invention. r

Fig. v1 shows a meridian sectional view of a potential distribution which fulfills the formula in cylinder coordinates,

k, L and R being three constants. By differentiation of the above expression with respect to r, it is found that for r=R the radial field is zero, consequently on a cylinder having a radius R and an axis ZZ in the figure. On this cylinder the potential distribution fulfills the parabolic ratio V=k(L z which is to be taken to mean that the field intensity varies linearly in relation to the poten- *tial maximum, as is required for the repeated passage back and forth of the electrons. In Fig. 1 a number of sections of equipotential surfaces are designated by full lines. The potential surface of two sheets is designated by heavy lines and comprises the outer sheet M'wM in the form of a diabolo and the inner sheet N'wN in the form of a spindle. The double points of these two surfaces thus located on a circle having a radius R in a plane normal to the axis ZZ. The useful part of the field is indicated by the chain-dotted circle having a radius S.

Fig. 2 shows the electrode system of the tube the electrode surfaces of which conform as far as possible with the equipotential surfaces of Fig. 1. The annular cathode is designated 1 and a grid 1', two acceleration anodes 2 and 3 direct the electron beam parallel to the axis ZZ so that the electron beam 4 is given the shape of a cylinder surface and moves through the annular apertures 2 and 3 in the electrodes 2 and 3. The electron beam then moves through an annular resonator 5 which comprises two truncated cone surfaces 5 and 5" united by a curved surface 5", the brake electrode being designated 6 and the reflection electrode 7. Near the axis is arranged an electrode 8 which collects the electrons which have lost their velocit The modulation space 9 is contained between the two edges of the resonator and has a fiat boxshape parallel to the plane of symmetry 1r. The walls 5' and 5" conform as far as possible with the outer part of the surface of two sheets M'wM. The brake space remote from the cathode is designated 10. A coupling loop 11 endures withdrawal of the high-frequency energy. In order that the electron beam may convey a sufiicient number of electrons it must have a thickness such on the cylinder surface that the electron beam moves between the cylinders having a radius 0.9 R and R respectively. With the exception of the cathode 1 and the grid 1' the surfaces of all the electrodes conform as far as possible with the equipotential surfaces of Fig. 1. However, as an alternative the resonator may be given the shape designated 51.

Referring to Fig. 3, the resonator is formed by the two sheets of the equipotential surface of Fig. l, M'wM and N'wN, that is to say the outer which is designated 5 and the inner which is designated 50, the coupling between the electron beam and the resonator being more tight than in the construction shown in Fig. 2.

'WhatIclairnis:

,1. An electrical device of the reflex klystron type comprising an electrode system which is rotationally-symmetric about a central axis, said electrode system including an annular cathode producing a hollow cylindrical electron beam coaxial with said central axis anddisplaced a certain radius therefrom and an acceleration and brake electrode system aligned with said cathode and cooperating therewith to produce a rotationally-symmetric cylindrical field centered about said central axis through which the cylindrical beam passes said field having a parabolic axial distribution and a radial distribution which produces a zero field at said radius whereby electrons in said beam are caused to move back and forth with an axial velocity determined by said parabolic axial distribution and are maintained at said radius by said zero field, and a toroidal cavity resonator having an annular gap surrounding said cylindrical electron beam between said cathode and brake electrode system and aligned therewith so that said beam passes through the gap and interacts therewith, at least said acceleration and brake electrode systems having a shape and configuration in the vicinity of said electron beam substantially coinciding with the equipotenti-al surfaces of said cylindrical parabolic field whereby the radial field intensity acting on said electron beam is substantially zero and. external beam focussing means become unnecessary.

2. An electrical device as set forth in claim 1 wherein the surfaces of the toroidal resonator in the vicinity of the electron beam also substantially coincide with equipotential surfaces of the cylindrical parabolic field.

3. An electrical device as set forth in claim 2 wherein the toroidal resonator is constituted of a pair of truncated cone surfaces whose walls are joined by ;a curved surface.

References Cited in the file of this patent UNITED STATES PATENTS 2,124,270 Broadway July 19, 193.8 2,268,194 Glass Dec. 30, 1941 2,409,693 Okress Oct. 22, 1946 2,413,251 Smith Dec. 24, 1946 2,445,771 Fremlin etal July 27, 1948 2,466,063 Varian .Q Apr. 5, 1949 2,531,195 l Broadway Nov. 21, 1950 

